The present invention relates generally to endoluminal grafts or xe2x80x9cstentsxe2x80x9d and, more specifically, to a stent delivery system or xe2x80x9cintroducerxe2x80x9d for deploying a stent inside of a prosthetic graft without interrupting fluid flow during deployment and a method for such deployment.
A stent is an elongated device used to support an intraluminal wall. In the case of a vascular stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. An intraluminal prosthesis may comprise a stent that carries a prosthetic layer of graft material. Such a prosthesis may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, an intraluminal stent or prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called xe2x80x9cminimally invasive techniquesxe2x80x9d in which the stent, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a stent deployment system or xe2x80x9cintroducerxe2x80x9d to the site where it is required. The introducer may enter the body through the patient""s skin, or by a xe2x80x9ccut downxe2x80x9d technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the stent deployment location, the introducer is manipulated to cause the stent to be released from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the stent), whereupon the stent expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stents are typically expanded by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Referring now to a stent deployment system of the prior art in FIG. 1, there is shown an endoluminal prosthesis 10 comprising a wire stent 12 affixed along its length to an outer graft cover 14, the graft and stent compressed inside outer sheath 16 (shown in cross-section). During the deployment process of endoluminal prosthesis 10 in a body lumen 20, such as a blood vessel, outer sheath 16 is retracted, and stent 12 expands against the walls 19 of the lumen 20 (shown in cross-section). During the expansion process, the partially-deployed, covered section 22 at distal end 23 and middle section 25 of integral stent/graft prosthesis 10 can block the flow of blood along arrow A temporarily until proximal end 24 is released from the sheath. As used herein, xe2x80x9cproximalxe2x80x9d is defined as meaning xe2x80x9ccloser to the end of the introducer remaining outside the bodyxe2x80x9d, whereas xe2x80x9cdistalxe2x80x9d is defined as meaning xe2x80x9cfarther from the end of the introducer remaining outside the bodyxe2x80x9d. During deployment, the pressure of obstructed blood flow at covered section 22 may cause the prosthesis to migrate away from its intended location or become longitudinally compressed. If for some reason the deployment procedure becomes protracted, the blood flow blocked by covered section 22 may impart serious stress upon the patient. Thus, it is desirable to provide for unobstructed blood flow throughout the stent deployment process.
A construction known to the inventor prior to this invention comprises a device shown in FIG. 2 comprising stent 12xe2x80x2 and outer graft cover 14xe2x80x2 joined by a connection 30 to stent 12xe2x80x2 proximal the distal end 23 thereof. Prior to deployment, stent 12xe2x80x2 and graft liner 14xe2x80x2 are restrained in a compressed configuration by an outer sheath 16xe2x80x2 surrounding both the stent and the liner, and by an inner sheath 38 disposed between stent 12xe2x80x2 and liner 14xe2x80x2 proximally of connection 30. Deployment of this prosthesis is effected by first retracting outer sheath 16xe2x80x2, allowing distal portion of stent 12xe2x80x2 and then cover 14xe2x80x2 to fully expand independently. Stent 12xe2x80x2 is subsequently fully expanded proximal of the connection point by retracting inner sheath 38. During deployment of this device, blood flow can continue as indicated by arrows B.
The introducer construction having two sheaths as described above necessarily requires an introducer of somewhat larger diameter and lesser flexibility than most such introducers known in the art having only a single sheath.
The present invention provides a flexible, single-sheath, low-profile delivery system for deployment of a stent inside of a biocompatible graft cover in a distal deployment location in a body lumen from a proximal access location outside the body lumen. The delivery system comprises a stent sheath having a distal end located upstream relative to the fluid flow; a compressed stent underlying the stent sheath, the stent having a proximal end housed within the stent sheath and a distal end; and a compressed biocompatible graft cover overlying the stent sheath along the length of the stent and releasably retained in a compressed state surrounding the sheath. The graft has a distal end attached to the stent at or proximal the stent distal end and an outer surface exposed to the interior space of the lumen during deployment. The stent distal end may be spaced distally from the stent sheath distal end and graft attachment, in which case the delivery system may further comprise a tip sheath overlying the stent distal end and an inner core, optionally having a guidewire lumen therein, attached to the tip and extending axially through the stent. A pusher underlies the stent sheath proximal the stent. The pusher distal end may be rounded. The inner core and attached tip sheath may be attached distally to the pusher, or the pusher may have an inner lumen extending axially therethrough, wherein the inner core extends axially through the pusher inner lumen.
The stent delivery system further may comprise a temporary, protective wrapper over the biocompatible graft, the wrapper adapted to be removed prior to insertion of the delivery system into the body lumen. The compressed biocompatible graft may further comprise a proximal end attached to the stent sheath by a releasable attachment, such as a suture, adapted to be released during deployment of the stent. The suture may be adapted for release by being secured with a slip-knot adapted to be untied during stent deployment, by the delivery system further comprising a balloon adapted for breaking the suture upon inflation of the balloon, or by the pusher further comprising a cutter, such as a sharpened hypotube, adapted for severing the suture upon movement of the pusher relative to the stent sheath.
Specifically, the stent sheath may have a suture connection point, such as a pair of tie-holes, in its circumference and radially-opposite first and second through-holes, with the pusher having a window in its distal end aligned with the stent sheath through-holes and having the cutter proximally located therein. In such a configuration, the opposite ends of the suture are attached to the suture connection point, and an intermediate section of the suture is threaded through the graft in one or more locations, through the sheath through-holes, and through the pusher window.
The invention further comprises a method for endoluminally deploying a stent and overlying biocompatible graft cover without obstructing fluid flow during deployment, as follows. First, the stent and graft are compressed and loaded into a single-sheath-profile stent delivery system as described herein. Then, the stent delivery system is inserted into a body lumen and navigated through the lumen until the stent is at a desired deployment location. Next, the stent sheath is proximally displaced relative to the stent distal end, the stent distal end becomes expanded, and endoluminal fluid flows between the stent sheath and the graft so that the graft becomes radially distanced from the stent sheath. Finally, deployment of the stent is completed so that it biases the graft against the body lumen.
Where the stent delivery system further comprises a tip having a tip sheath overlying the distal end of the stent and attached to an inner core extending axially through the stent, the method further comprises, prior to proximally displacing the stent sheath relative to the stent, first releasing the stent distal end from the tip sheath by displacing the inner core distally relative to the stent sheath. Where the pusher is attached to the inner core, displacing the inner core distally relative to the stent sheath comprises a single, continuous, proximal retraction of the stent sheath that also displaces the pusher distally relative to the stent sheath to deploy the stent. Where the pusher has an inner lumen axially therethrough through which the inner core is mounted, displacing the inner core distally relative to the stent sheath comprises first advancing the inner core distally relative to the stent sheath to release the stent distal end from the tip sheath, and then retracting the stent sheath to deploy the stent. Where the proximal end of the graft is attached to the sheath with a releasable attachment such as a suture, the attachment is released prior to endoluminal fluid flowing between the graft and the sheath. Where the releasable attachment is a suture, the step of moving the stent sheath relative to the pusher may cut the suture.
The method may further comprise suturing the graft to the stent sheath by the steps of anchoring a first end of the suture through the tie-holes, extending the suture along the stent sheath; piercing the graft one or more times with the suture; extending the suture along the stent sheath; entering the stent sheath radially through one of the through-holes, extending the suture through the pusher window, and exiting the stent sheath through the opposite through-hole; extending the suture along the stent sheath; piercing the graft one or more times with the suture; extending the suture semi-circumferentially around the sheath; and anchoring a second end of the suture to the tie-holes.
After deployment, the stent delivery system may be prepared for withdrawal by advancing the pusher into the tip sheath and advancing the stent sheath until the distal end of the stent sheath is adjacent the proximal end of the tip sheath, and then withdrawn. Prior to insertion into the body, the stent sheath may be locked to the pusher and the inner core biased under slight tension and locked to the pusher. In such case, deployment further comprises unlocking the inner core from the pusher prior to moving the inner core distally and unlocking the stent sheath from the pusher prior to retracting the stent sheath.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.